Sylvatic Canine Morbillivirus in Captive Panthera Highlights Viral Promiscuity and the Need for Better Prevention Strategies

Abstract

Canine Distemper Virus (CDV) is a multi-host morbillivirus that infects virtually all Carnivora and a few non-human primates. Here we describe a CDV outbreak in an exotic felid rescue center that led to the death of eight felids in the genus Panthera. Similar to domestic dogs and in contrast to previously described CDV cases in Panthera, severe pneumonia was the primary lesion and no viral antigens or CDV-like lesions were detected in the central nervous system. Four tigers succumbed to opportunistic infections. Viral hemagglutinin (H)-gene sequence was up to 99% similar to strains circulating contemporaneously in regional wildlife. CDV lesions in raccoons and skunk were primarily encephalitis. A few affected felids had at least one previous vaccination for CDV, while most felids at the center were vaccinated during the outbreak. Panthera sharing a fence or enclosure with infected conspecifics had significantly higher chances of getting sick or dying, suggesting tiger-tiger spread was more likely than recurrent spillover. Prior vaccination was incomplete and likely not protective. This outbreak highlights the need for further understanding of CDV epidemiology for species conservation and public health.

Keywords: Panthera; canine distemper virus; lion; outbreak; pneumonia; spillover; tiger; vaccine.

Figure 1

Canine distemper virus-typical intranuclear and intracytoplasmic, bright eosinophilic viral inclusions in multiple organs of Panthera: (a,b) Lion, lung with marked type II pneumocyte hyperplasia and syncytial cells containing viral inclusions (arrows, Hematoxylin and Eosin staining (H&E) and CDV-IHC); (c) Tiger #7, Renal pelvis, epithelial cells contain intracytoplasmic and intranuclear viral inclusions (arrows, H&E); (d) Tiger #7, pancreas, numerous exocrine epithelial cells contain viral inclusions (arrow, H&E).

Figure 2

Opportunistic infections recorded in Panthera: (a, H&E) Tiger #5, lung, type II pneumocytes and macrophages are markedly enlarged (up to 70 μm in diameter) and filled with an intracytoplasmic parasitopohorus vacuole that contains numerous 2–4 μm, round to fusiform, basophilic tachyzoites. Inset is the IHC for Toxoplasma gondii, which confirms strong immunoreactivity within infected cells. (b, H&E) Tiger #6, lung, alveolar macrophages and few type II pneumocytes are enlarged and contain numerous intracytoplasmic round to ovoid, pale basophilic, 2–5 μm in diameter yeasts with 1–2 μm thick walls (arrows) that are also GMS-positive (black, inset). Microbiology culture was most compatible with Histoplasma capsulatum.

Figure 3

Schematic map of the rescue center, which was divided in two epidemiologic units A/Front (in pink) and B/Field (in turquoise). Inset has the order of the seven cases within unit A. Only one CDV-confirmed case was registered in Unit B.